A polysilicon nanoelectrospray-mass spectrometry source based on a microfluidic capillary slot

A novel micromachining process for the fabrication of miniaturised polysilicon-based nanoelectrospray ionisation-mass spectrometry (nanoESI-MS) sources is developed in this paper. The nanoESI source topology is composed of two highly planar triangular free-standing cantilevers which form a microfluidic capillary slot having a width (w) and a height (h). A combination of low pressure chemical vapour deposition (LPCVD), pattern-transfer, reactive ion etching (RIE) and sacrificial layer etching is used to fabricate the nanoESI sources which project horizontally beyond the edge of a silicon substrate by a length of 800 μm. NanoESI sources having two different capillary slot dimensions are tested: w×h = 1.8 μm × 2 μm and 2.5 μm × 5 μm. The sources have been tested on an ion trap mass spectrometer (MS) using a standard peptide sample (Glu-Fibrinopeptide B) at a concentration of 1 μM. The resultant mass spectra show that the microfabricated capillary slot-based nanoESI sources presented here demonstrate state-of-the-art performances in terms of electrospray ionisation voltage (0.7 kV) and test solution aqueous concentration (90% H2O).